Japanese Patent No. 5674190, for example, describes a sensor connection structure disposed in a pipe unit (manifold). The pipe unit includes a main pipe and a plurality of branch pipes connected to the left and right of the main pipe. Each of the branch pipes is provided with a valve such as a steam trap. In the pipe unit, drain (condensate) generated by condensation of steam flows from the branch pipes into the main pipe and is collected therein. The sensor connection structure includes a plurality of sensors disposed on the steam traps and a terminal unit disposed on the main pipe. Each of the sensors detects operating states (vibrations and temperature) of a corresponding one of the steam traps. The sensors are connected to the terminal unit by electric wires (lead wires), and information on the operating states detected by the sensors is sent to the terminal unit. The terminal unit transmits and receives information on the operating states to/from a central management device. In this manner, the operating states of the steam traps are monitored.
In the sensor connection structure described in Japanese Patent No. 5674190, the terminal unit is connected to the sensors by electric wires so that wiring to the terminal unit might become complex. To avoid this complexity, it is conceivable to perform wireless communication between the terminal unit and the sensors. In this case, however, transmission and reception of radio waves might be difficult in some installation conditions of the terminal unit and the sensors, and thus, accuracy in monitoring operating states of the valves might be impaired.
A technique disclosed in the present application has been made in view of the foregoing situations, and has an object to provide a sensor connection structure that can ensure transmission, to a terminal unit, of information on operating states detected by a plurality of sensors while reducing complexity of wiring between the sensors and the terminal unit.